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+ (___()'`; Rusty's Remarkably Unreliable Guide to Lguest
+ /, /` - or, A Young Coder's Illustrated Hypervisor
+ \\"--\\ http://lguest.ozlabs.org
+Lguest is designed to be a minimal 32-bit x86 hypervisor for the Linux kernel,
+for Linux developers and users to experiment with virtualization with the
+minimum of complexity. Nonetheless, it should have sufficient features to
+make it useful for specific tasks, and, of course, you are encouraged to fork
+and enhance it (see drivers/lguest/README).
+- Kernel module which runs in a normal kernel.
+- Simple I/O model for communication.
+- Simple program to create new guests.
+- Logo contains cute puppies: http://lguest.ozlabs.org
+- Fun to hack on.
+- No ABI: being tied to a specific kernel anyway, you can change anything.
+- Many opportunities for improvement or feature implementation.
+- The easiest way to run lguest is to use same kernel as guest and host.
+ You can configure them differently, but usually it's easiest not to.
+ You will need to configure your kernel with the following options:
+ "General setup":
+ "Prompt for development and/or incomplete code/drivers" = Y
+ "Processor type and features":
+ "Paravirtualized guest support" = Y
+ "Lguest guest support" = Y
+ "High Memory Support" = off/4GB
+ "Alignment value to which kernel should be aligned" = 0x100000
+ (CONFIG_PARAVIRT=y, CONFIG_LGUEST_GUEST=y, CONFIG_HIGHMEM64G=n and
+ "Device Drivers":
+ "Block devices"
+ "Virtio block driver (EXPERIMENTAL)" = M/Y
+ "Network device support"
+ "Universal TUN/TAP device driver support" = M/Y
+ "Virtio network driver (EXPERIMENTAL)" = M/Y
+ (CONFIG_VIRTIO_BLK=m, CONFIG_VIRTIO_NET=m and CONFIG_TUN=m)
+ "Linux hypervisor example code" = M/Y
+- A tool called "lguest" is available in this directory: type "make"
+ to build it. If you didn't build your kernel in-tree, use "make
+- Create or find a root disk image. There are several useful ones
+ around, such as the xm-test tiny root image at
+ For more serious work, I usually use a distribution ISO image and
+ install it under qemu, then make multiple copies:
+ dd if=/dev/zero of=rootfile bs=1M count=2048
+ qemu -cdrom image.iso -hda rootfile -net user -net nic -boot d
+ Make sure that you install a getty on /dev/hvc0 if you want to log in on the
+- "modprobe lg" if you built it as a module.
+- Run an lguest as root:
+ Documentation/virtual/lguest/lguest 64 vmlinux --tunnet=192.168.19.1 \
+ --block=rootfile root=/dev/vda
+ 64: the amount of memory to use, in MB.
+ vmlinux: the kernel image found in the top of your build directory. You
+ can also use a standard bzImage.
+ --tunnet=192.168.19.1: configures a "tap" device for networking with this
+ IP address.
+ --block=rootfile: a file or block device which becomes /dev/vda
+ inside the guest.
+ root=/dev/vda: this (and anything else on the command line) are
+ kernel boot parameters.
+- Configuring networking. I usually have the host masquerade, using
+ "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" and "echo 1 >
+ /proc/sys/net/ipv4/ip_forward". In this example, I would configure
+ eth0 inside the guest at 192.168.19.2.
+ Another method is to bridge the tap device to an external interface
+ using --tunnet=bridge:<bridgename>, and perhaps run dhcp on the guest
+ to obtain an IP address. The bridge needs to be configured first:
+ this option simply adds the tap interface to it.
+ A simple example on my system:
+ ifconfig eth0 0.0.0.0
+ brctl addbr lg0
+ ifconfig lg0 up
+ brctl addif lg0 eth0
+ dhclient lg0
+ Then use --tunnet=bridge:lg0 when launching the guest.
+ for general information on how to get bridging to work.
+- Random number generation. Using the --rng option will provide a
+ /dev/hwrng in the guest that will read from the host's /dev/random.
+ Use this option in conjunction with rng-tools (see ../hw_random.txt)
+ to provide entropy to the guest kernel's /dev/random.
+There is a helpful mailing list at http://ozlabs.org/mailman/listinfo/lguest
+Rusty Russell firstname.lastname@example.org.